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Thread: best antenna

  1. #2401
    Captain abcd567's Avatar
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    Due to yesterday's abnormal graph, I checked my system and found a defective (dodgy/intermittent) connector. I replaced the connector and repeated yesterday's test, and results are now normal as follows.

    1) When The ¼ λ whip was replaced by Franklin whip, there was a distinct drop in performance to about 40%.

    2) When crude impedance matching was added to the Franklin Spider, there was a distinct increase in performance, jumping up from 40% to 85% of Spider.

    Now I have to optimize the matching network by:

    1) Using an adjustable trimmer capacitor 2 - 5 pF instead of fixed ceramic capacitor of 2 pF.

    AND

    2) Try three lengths of transmission lines (i.e 205 mm, 210 mm & 215 mm) between antenna & capacitor.

    I hope I will be able to achieve optimum matching, in which case the Franklin Spider's performance will (hopefully) exceed Spider's performance.




    .
    Last edited by abcd567; 2015-07-19 at 02:44.

  2. #2402
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    I made also this Franklin Spider antenna today. Lets see how it performs. And thanks abcd567 at good antenna tips
    F-EFRO3

  3. #2403
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    Quote Originally Posted by AzKo View Post
    I made also this Franklin Spider antenna today. Lets see how it performs. And thanks abcd567 at good antenna tips
    The Franklin Spider is inferior to Spider if impedance matching is not used, but can be made superior to it by impedance matching, as shown in above post.

    Today I have tried two tweaks in values of the two parameters of impedance matching as below:

    (1) Soldered a third 1 pF Capacitor in parallel with existing two, increasing the total value of Capacitor from 2 pF to 3 pF

    (2) Tried two different lengths of transmission line between the Antenna & the Capacitor. Original was 210 mm (including length of connectors at both ends). I made two more, one 225 mm (including length of connectors at both ends), other 240 mm (including length of connectors at both ends).

    The combination of 3 pF Capacitor & 240 mm Transmission Line (including length of connectors at both ends) between Capacitor & Antenna resulted in Franklin Spider surpassing the performance of Spider.

    Since each built of DIY antenna is slightly different, these values (240 mm / 3 pF) may not be optimum for every one, but sure will be close to optimum, provided RG6 Coax cable (with VF 0.83 to 0.85) is used as transmission line piece between Antenna & Capacitor, shown in photo in my post #2395.
    Last edited by abcd567; 2015-07-20 at 01:29.

  4. #2404
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    This is my 2nd quarter wave antenna with 8 legs, new build have not install yet , first one is on duty .
    IMG_5535.jpg

    Another antenna I made month ago , it prove my solder skill pretty bad .
    IMG_5463.jpg

  5. #2405
    Captain abcd567's Avatar
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    Trial Runs for Comparison of FRANKLIN SPIDER (With Impedance Matching added), Spider, and Franklin Spider.



  6. #2406
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    Quote Originally Posted by iamnothere View Post
    This is my 2nd quarter wave antenna with 8 legs, new build have not install yet , first one is on duty .
    IMG_5535.jpg

    Another antenna I made month ago , it prove my solder skill pretty bad .
    IMG_5463.jpg
    Well done! Keep experimenting. That is how you are going to learn & find the best antenna built for your system. Dont worry about soldering. Many of us (including me) have worst soldering skill than your's.

  7. #2407
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    Build spider today when finally get some stuff to build something. And im not also so good solder. But main thing is that antenna is working

    2015-07-20 22.39.17.jpg
    F-EFRO3

  8. #2408
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    Quote Originally Posted by AzKo View Post
    Build spider today when finally get some stuff to build something. And im not also so good solder. But main thing is that antenna is working

    2015-07-20 22.39.17.jpg
    Good work!

    Spider is one of the easiest and very reliable antenna for begginners. In fact all antennas with a ¼ wavelength (69mm) whip and a groundplane (metal disc, horizontal radials, slanting radials, or a food/drink can, also known as Cantenna) are ideal for beginners.

    The reasons are:

    (1) These antennas are naturally resonant, i.e. have an impedance close to 75 ohms, which matches with the Coaxial cable, Amplifier & Receiver (dvb-t) impedance and gives a swr less than 1.5, a highly desireable situation.

    (2) These antennas have high dimensional tolerance, so few mm error in length of whip or radials or few degrees error in bending down the radials does not appreciably degrade its performance.

    Dont worry about soldering. The antenna works good even if the soldering is not very good.

    Please click the link below to see 4 different antennas, all with ¼ wavelength whip, but each with different methods of providing groundplane.


    http://forum.flightradar24.com/threa...-FOR-BEGINNERS
    Last edited by abcd567; 2015-07-20 at 23:38.

  9. #2409
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    Thanks , abcd567

  10. #2410
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    Look what I caught on my receiver:
    A Crazy Pilot Taxiing Under Influence of Alcohol?
    No it is an airport maintenance vehicle fitted with ADS-B transponder!


    Last edited by abcd567; 2015-07-22 at 07:15.

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